1. Field of the Invention
The present invention relates to a numerically-controlled machine tool provided with a spindle error compensation function and the spindle error compensating method for the numerically-controlled machine tool.
2. Description of the Related Art
In a machine tool provided with a spindle fixed to a linear moving axis or a rotary axis and a table having one or more linear moving axes or rotary axes and also provided with a numerical controller for controlling an operation of the spindle and the table, when a vertical or parallel machining is to be performed on a machining surface of a workpiece with high accuracy, highly accurate working can be realized by installing the workpiece or the machining surface perpendicularly or parallelly with accuracy with respect to the moving axis.
However, when the workpiece is to be machined by being attached to the machine tool by using a jig such as a stock vice or a chuck, it is likely that the machining surface is inclined with respect to the moving axis and cannot be necessarily perpendicular or parallel, and manual fine adjustment is needed each time.
In response to that, a method in which the inclination of the workpiece or the machining surface is measured before machining, and a table on which the workpiece is installed is subjected to inclination compensation according to inclination acquired by the measurement for highly accurate machining of the machining surface is disclosed in Japanese Patent Application Laid-Open No. 2010-201581.
However, the technology disclosed in Japanese Patent Application Laid-Open No. 2010-201581 is only to compensate inclination of the workpiece, and if the spindle holding a machining tool is installed perpendicularly or parallelly with high accuracy with respect to the table on which the workpiece is placed, highly accurate machining is possible as illustrated in FIGS. 16A and 16B, but if the spindle is not installed perpendicular to or parallel to the table, it causes occurrence of defective machining such as a step in milling as illustrated in FIGS. 17A, 17B, and 17C and deformation of a drill in drilling.
FIG. 16A illustrates an example of two-stage pocket machining by end mill machining on a workpiece placed on the table. FIG. 16B illustrates an example of drilling on a workpiece placed on the table. FIG. 17A illustrates an example of pocket machining in two stages by end mill machining on a workpiece placed on the table. FIG. 17B illustrates an example of drilling on a workpiece placed on the table. As illustrated in FIGS. 17A, 17B, and 17C, if the spindle is not perpendicular to the workpiece on the table, defective machining or breakage of a tool is caused.